Dual-function nano-sized particles

ABSTRACT

Dual-function nano-sized particles or nanoparticles may be effective at fixating or reducing fines migration and they may facilitate identification of a particular zone in a well having more than one zone. In some embodiments the dual-function nanoparticles are tagged with a detectable material that is distinguishable from the composition of the primary nanoparticle component. In these embodiments, the taggant material rather than the primary component of the nanoparticles may be used to enable identification of a particular zone. The nanoparticles (with or without taggant) may be added to a treatment fluid containing carrier particles such as proppant. The treatment fluid is pumped downhole to one of the zones; each zone receiving its own unique or uniquely-tagged nanoparticles. Should one of the zones fail, the composition of the nanoparticles (or its taggant) produced on the carrier particles may be correlated to the zone from which it was received, and hence produced.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No. 12/818,927filed Jun. 18, 2010, issued Jan. 10, 2017 as U.S. Pat. No. 9,540,562,which is a continuation-in-part application of U.S. Ser. No. 11/931,706filed Oct. 31, 2007 and U.S. Ser. No. 11/849,820 filed Sep. 4, 2007, thelatter which claims the benefit of U.S. Provisional Patent Application60/845,916 filed Sep. 20, 2006, and in turn is a continuation-in-partapplication of U.S. Ser. No. 11/125,465 filed May 10, 2005, issued Mar.18, 2008, as U.S. Pat. No. 7,343,972 which in turn claims the benefit ofU.S. Provisional Patent Application 60/570,601 filed May 13, 2004 and isa continuation-in-part application of U.S. Ser. No. 11/755,581 filed May30, 2007, issued Jun. 23, 2009 as U.S. Pat. No. 7,550,413, which in turnclaims the benefit of U.S. Provisional Application No. 60/815,693 filedJun. 22, 2006.

TECHNICAL FIELD

Non-limiting embodiments as described herein relate to methods andcompositions utilizing dual-function nano-sized particles, and moreparticularly relate, in non-limiting embodiments, to methods andcompositions using nano-sized particles effective at reducing finesmigration within subterranean formations, and if there is undesired flowback from one or more zones in a well having more than one zone,identifying the zone or zones from which the undesired flow backoriginated, or both during hydrocarbon recovery operations.

BACKGROUND

Hydrocarbons sometimes exist in reservoirs in subterranean rockformations. Generally, to produce the hydrocarbons from the formation, awellbore is drilled in the formation and hydrocarbons travel from theformation to the wellbore through pores in the formation. The better theconnectivity of the pores in the formation (permeability), the betterthe hydrocarbon production.

Production may be seriously hindered by blockages due to presence of ormigration of fines in the formation. The migration of fines involves themovement of fine clay and/or non-clay particles (e.g. quartz, amorphoussilica, feldspars, zeolites, carbonates, salts and micas) or similarmaterials within a subterranean reservoir formation due to drag andother forces during production of hydrocarbons or water. Fines migrationmay result from an unconsolidated or inherently unstable formation, orfrom the use of an incompatible treatment fluid that liberates fineparticles. Fines migration may cause the very small particles suspendedin the produced fluid to bridge the pore throats near the wellbore,thereby reducing well productivity. Damage created by fines is typicallylocated within a radius of about 3 to 5 feet (about 1 to 2 meters) ofthe wellbore, and may occur in gravel-pack completions and otheroperations.

Fines migration is a complex phenomenon governed largely by mineralogy,permeability, salinity and pH changes, as well as drag forces created byflow velocity, turbulence and fluid viscosity, as described in detail inJ. Hibbeler, et al., “An Integrated Long-Term Solution for MigratoryFines Damage,” SPE 81017, SPE Latin American and Caribbean PetroleumEngineering Conference, Port-of-Spain, Trinidad, West Indies, 27-30 Apr.2003, incorporated herein by reference in its entirety. The authors notethat mobilization of fines can severely damage a well's productivity,and that fines damage is a multi-parameter, complex issue that may bedue to one or more of the following downhole phenomena: (1) high flowrates, particularly abrupt changes to flow rates; (2) wettabilityeffects, (3) ion exchange; (4) two-phase flow, particularly due toturbulence that destabilize fines in the near-wellbore region; and (5)acidizing treatments of the wrong type or volume which can cause fines.

J. Hibbeler, et al. note that fines, especially clays, tend to flowdepending on their wettability, and since fines are typically water-wet,the introduction of water may trigger fines migration. However, theynote that clay particles may become oil-wet or partially oil-wet, due toan outside influence, and thus the fines and clay particles may becomeattracted to and immersed in the oil phase. The authors also note thatall clays have an overall negative charge and that during salinitydecrease, pH increases in-situ due to ion exchange. A pH increase mayalso be induced via an injected fluid. As pH increases, surfacepotential of fines increases until de-flocculation and detachmentoccurs, aggravating fines migration.

Fines fixation has become troublesome during oil and gas production andduring many oil and gas recovery operations, such as acidizing,fracturing, gravel packing, and secondary and tertiary recoveryprocedures. Hydraulic fracturing is a method of using pump rate andhydraulic pressure to fracture or crack a subterranean formation. Oncethe crack or cracks are made, high permeability proppant, relative tothe formation permeability, is pumped into the fracture to prop open thecrack. When the applied pump rates and pressures are reduced or removedfrom the formation, the crack or fracture cannot close or healcompletely because the high permeability proppant keeps the crack open.The propped crack or fracture provides a high permeability pathconnecting the producing wellbore to a larger formation area to enhancethe production of hydrocarbons.

Gravel packing is a sand-control method employed to prevent theproduction of formation sand. In gravel pack operations, a steel screenis placed in the wellbore and the surrounding annulus packed with agravel of a specific size designed to prevent the passage of formationsand. The goal is to stabilize the formation while causing minimalimpairment to well productivity. Operations combining fracturing andgravel packing are termed “frac packs”.

Hydraulic fracturing, gravel packing, and/or frac pack treatments mayfail such that proppant, gravel, or both are produced into the well. Ifthe proppant, for example, flows back into the well it cannot keep thefracture propped open. This type of failure may be repaired orremediated if the engineers know where the failure occurred in the well.This may be easy enough if the well has only one zone such as a fracturezone, but if the well has more than one zone, it is typically difficultto determine which zone failed.

Thus, it would be desirable if methods and/or compositions would bedevised to help identify a failed zone in a well having more than onezone using material that are also effective at fixing or stabilizingfines within a subterranean formation so that their migration isreduced, inhibited or eliminated.

SUMMARY

In a non-limiting aspect, a method is provided that includes determiningwhich zone in a well having more than one treatment-based zone carrierparticles were produced from. The carrier particles have nano-sizedparticles disposed thereon, and the nano-sized particles are effectiveto reduce fines migration in a subterranean formation and have a meanparticle size of 1000 nm or less; a primary component selected from thegroup consisting of alkaline earth metal oxides, alkaline earth metalhydroxides, transition metal oxides, transition metal hydroxides,post-transition metal oxides, post-transition metal hydroxides,piezoelectric crystals, pyroelectric crystals, and mixtures thereof. Thecomposition of the nano-sized particles is indicative of the zone fromwhich the carrier particles were produced. In some non-limitingembodiments, the nano-sized particles also include a detectable taggantselected from the group consisting of alkaline earth metals, transitionmetals, post-transition metals, lanthanoids, and mixtures thereof. Theselected taggant is selected to be distinguishable from the primarycomponent and to be indicative of one of the more than one zone.

In another non-limiting aspect, a treatment fluid is provided thatcomprises a base fluid selected from the group consisting of water-basedfluids, alcohol-based fluids and oil-based fluids. The treatment fluidalso comprises carrier particles selected from the group consisting ofsand, gravel, ceramic beads, glass beads, and combinations thereof, andan effective amount of a particulate additive to reduce fines migrationand to facilitate identification of a zone in a well having more thanone treatment-based zone. The particulate additive has a mean particlesize of 1000 nm or less; a primary component selected from the groupconsisting of alkaline earth metal oxides, alkaline earth metalhydroxides, transition metal oxides, transition metal hydroxides,post-transition metal oxides, post-transition metal hydroxides,piezoelectric crystals, pyroelectric crystals, and mixtures thereof; anda taggant selected from the group consisting of alkaline earth metals,transition metals, post-transition metals, lanthanoids; and mixturesthereof, where the taggant is selected to be distinguishable from theprimary component.

In an additional non-limiting aspect, coated carrier particles areprovided. The coated carrier particles comprise carrier particlesselected from the group consisting of sand, gravel, ceramic beads, glassbeads, and combinations thereof; nanoparticles disposed on the carrierparticles with a coating agent. The nanoparticles have a mean particlesize of 1000 nm or less; a primary component selected from the groupconsisting of alkaline earth metal oxides, alkaline earth metalhydroxides, transition metal oxides, transition metal hydroxides,post-transition metal oxides, post-transition metal hydroxides,piezoelectric crystals, pyroelectric crystals, and mixtures thereof; anda taggant selected from the group consisting of alkaline earth metals,transition metals, post-transition metals, lanthanoids, and mixturesthereof; where the taggant is selected to be distinguishable from theprimary component.

In yet another non-limiting aspect, a method for reducing finesmigration within a subterranean formation and for distinguishing betweenzones in a well having more than one treatment-based zone is provided.The well is drilled in the subterranean formation. Each zone in the wellreceives carrier particles that carry an amount of nano-sized particleseffective to reduced fines migration in the subterranean formation. Thenano-sized particles have a mean particle size of 1000 nm or less, areselected from the group consisting of alkaline earth metal oxides,alkaline earth metal hydroxides, transition metal oxides, transitionmetal hydroxides, post-transition metal oxides, post-transition metalhydroxides, piezoelectric crystals, pyroelectric crystals, and mixturesthereof. The carrier particles received in each zone of the well includenano-sized particles that are chemically unique to that zone.

The particulate additive, also referred to herein as nano-sizedparticles or nanoparticles may fixate or flocculate fines, such as clayand non-clay particles to keep or restrict or reduce the fine particlesfrom moving in, for example, a propped hydraulic fracture in asubterranean formation. In this non-limiting example, the nano-sizedparticles, which coat on the proppant particles, may bind or fix thefines to the proppant particles, such as 20/40 mesh ceramic proppants,so that both the formation fines and the nanoparticles remain on theproppant particles and do not travel or are restrained to the point thatfine migration damage to the near-wellbore region is minimized.

Should for some reason carrier particles placed during a treatment, suchas proppant within a fracture hydraulic fracturing, be produced or flowback into the wellbore they may be detected via the composition of thenano-size particulate additive and/or via a traceable taggant that maybe incorporated into the body of the nano-size particulate additive,coated thereon, or both. Detecting such nanoparticles is useful insituations where a well has more than one zone, such as sequentialmulti-stage fracturing treatments in horizontally completed shale ortight gas completions. For instance, for each zone in the well,fines-fixing nanoparticles are introduced into the zone, where thenano-sized particles may carry a detectable taggant that is unique tothat zone and/or the nano-sized particle itself may be unique to thatzone. And if the nano-sized particles from one or more of the zonesshould flow back into the wellbore on produced proppant particles (orother carrier particle), a sample of the produced proppant containingthe uniquely-tagged and/or unique nanoparticles may be analyzed todetermine the identity of the nanoparticle(s)/taggant(s). Since thenano-sized particles for each zone may carry a unique taggant and/or maythemselves be unique, the zone from which the nanoparticles wereproduced may be determined.

DETAILED DESCRIPTION

Fines migration has been troublesome during oil and gas production, aswell as during many oil and gas recovery operations including, but notnecessarily limited to, acidizing, fracturing, gravel packing, secondaryand tertiary recovery operations, and the like. As discussed in SPE81017 referred to above, most of the fines that migrate and cause damagehave a charge, and most clay particles generally have an overallnegative charge. As defined herein, fines (i.e. formation fines) arenaturally occurring particles having particle size less than 37 microns(μm).

Nano-sized particles like magnesium oxide (MgO) may be used to fixateformation fines such as clay and quartz in subterranean hydrocarbonformations to inhibit, restrain, or prevent the fines from migrating tonear-wellbore regions to damage production of the hydrocarbons. Somenano-sized particles, also called nanoparticles herein, not only havehigh surface areas compared to their small sizes, but also haverelatively high surface charges that permit them to associate or connectother particles together, including other charged particles, but alsoother non-charged particles. In one non-limiting embodiment, theseassociations or connections between the fines and the nano-sizedparticles are due to electrical attractions and other intermolecularforces or effects.

In addition to fines migration being troublesome during oil and gasproduction and/or recovery operations, one or more of these operationsmay periodically fail. For instance, operations such as fracturing,gravel packing, and frac-packing may fail allowing undesired flow backor production of carrier particles such as proppant or gravel particlesinto the wellbore from, for example, the hydraulic fracture in theformation. As such, the intended treatment may not be effective and theproduced proppant or gravel or the like may cause additional damage suchas to the equipment.

Matters are further complicated if a well has more than one zone. In onenon-limiting example, the subterranean formation proximate a wellboremay be treated with more than one fracture treatment, each fracture areacorresponding with a zone. These types of zones may be formed in asequence where one zone is hydraulically fractured, and once completedanother zone is hydraulically fractured and completed, the patternrepeating until all frac jobs for the particular well are finished. Suchzones may be termed “fracture-based zones”. One example of a fracturecompletion system is FRAC-POINT™, which is available from Baker HughesIncorporated. Embodiments, however, are not limited to the forgoingexample, and zones are not limited to fracture-based zones—they may becharacterized by any type of interval, such as without limitation gravelpack and frac-pack based zones. If there is a failure in a dual ormulti-zonal well it may be very difficult to determine which zonefailed.

The nano-sized particles used to fixate formation fines and inhibit,restrain, or prevent such fines from migrating may also be used toidentify a defective zone in a well having more than one zone. Forinstance, nanoparticles may be disposed on carrier particles such asproppant, sand, gravel, and the like. The nanoparticles may or may notbe tagged with a detectable material. In embodiments where thenano-sized particles do not include taggant material, each zone receivesproppant carrying nanoparticles with a chemical make-up that is distinctfor that zone. Similarly, in embodiments where the nano-sized particlesinclude a taggant material, each zone receives proppant carrying taggednanoparticles where the taggant received in each zone is chemicallydistinct from that received in the other zone or zones. Thus, thenanoparticles may be used to fix formation fines and the chemicalcomposition of the nanoparticles, the taggant, or both may be used as anidentifier. In a simplified, non-limiting example, proppant having onetype of dual-function nanoparticles disposed thereon may be suspended ina base fluid and be pumped downhole to the zone being treated. Another,different zone may be treated in the same way except the proppantcarries another, different type of dual-function nanoparticles and/ortaggant material to the other downhole zone. While in the fractures, thenanoparticles fixate formation fines onto proppant particles. But shouldone or both of the zones fail for some reason (e.g. produce proppantfrom the hydraulic fracture), the proppant produced into the well may beanalyzed to determine which nanoparticle(s), taggant(s), or both arepresent on the proppant. The identity of such nanoparticle(s) and/ortaggant(s) on produced proppant may then be used to determine which zoneor zones they were produced from, hence where the failure(s) occurred.That is, dual-function nanoparticles (e.g. produced on proppant) may bechemically analyzed to provide information about their constituents,including the taggant if present. Since nanoparticles and/or taggantscan be chemically differentiated, and chemically distinct nanoparticlesand/or taggants will be used in different zones, chemical analysis ofthe nano-sized particles and/or taggants can facilitate identificationof the zone from which they originated. The nanoparticles are believedto provide both functions without damage to subterranean formations.

To analyze the composition of nanoparticles, taggant, or both, a samplecontaining produced proppant may be obtained. It is expected thatsamples will usually come from reservoir fluids, such as hydrocarbons,containing solids, such as proppant, that are produced to the surface.Alternatively, and without limitation, produced proppant samples may beobtained by mechanical sampling such as via a downhole wireline with asolids removal tool at the end, or by using a viscosified fluid to sweepout the wellbore. Generally, to sweep out the wellbore, a viscous pillis pumped from the surface using the existing tubing or a coiled tubingto wash out a wellbore. Regardless of how the proppant (or other carrierparticle) sample is obtained, it may be analyzed by any suitabledetection method such as, without limitation, inductively-coupled plasma(ICP), X-ray fluorescence (XRF), x-ray diffraction (XRD), andproton-induced X-ray emission.

Chemically, nano-sized particles or nanoparticles may be comprised ofmetal oxides and/or hydroxides. For example, dual-function nanoparticlesmay be comprised of materials selected from the group consisting ofalkaline earth metal oxides, alkaline earth metal hydroxides, transitionmetal oxides, transition metal hydroxides, post-transition metal oxides,post-transition metal hydroxides, and mixtures thereof. Embodiments,however, are not limited to metal oxides and/or hydroxides;piezoelectric crystals and pyroelectric crystals are also suitablematerials from which nanoparticles may be produced.

Magnesium oxide is a suitable material for making dual-functionnanoparticles. Magnesium oxide particles and powders are but one exampleof a suitable alkaline earth metal oxide and/or alkaline earth metalhydroxide particle. Other suitable alkaline earth metal oxides and/orhydroxides include elements in Group IIA of the previous IUPAC AmericanGroup notation, including without limitation, calcium (Ca), strontium(Sr), and barium (Ba).

Dual-function nanoparticles may also comprise oxides and/or hydroxidesof one or more “post-transition” metals such as without limitationaluminum (Al), gallium (Ga), indium (In), tin (Sn), thallium (TI), lead(Pb), and bismuth (Bi). In another non-limiting embodiment, nano-sizedparticles may be oxides and/or hydroxides of elements of Groups IIB andIIIB of the previous IUPAC American Group notation. These elementsinclude, but are not necessarily limited to, titanium (Ti), zirconium(Zr), cobalt (Co), nickel (Ni) and/or zinc (Zn). Non-limiting examplesof such suitable oxides include zinc oxide (ZnO), zirconium dioxide(ZrO₂), titanium dioxide (TiO₂), cobalt (II) oxide (CoO), and/or nickel(II) oxide (NiO).

Dual-function nano-sized particles may also be comprised ofpiezoelectric crystal particles (which include pyroelectric crystalparticles). Pyroelectric crystals generate electrical charges whenheated and piezoelectric crystals generate electrical charges whensqueezed, compressed, or pressed. In one non-limiting embodiment,specific suitable piezoelectric crystal particles may include, but arenot necessarily limited to, ZnO, berlinite (AIPO₄), lithium tantalate(LiTaO₃), gallium orthophosphate (GaPO₄), BaTiO₃, SrTiO₃, PbZrTiO₃,KNbO₃, LiNbO₃, LiTaO₃, BiFeO₃, sodium tungstate, Ba₂NaNb₅O₅, Pb₂KNb₅O₁₅,potassium sodium tartrate, tourmaline, topaz and mixtures thereof. Thetotal pyroelectric coefficient of ZnO is −9.4 C/m²K. ZnO and these othercrystals are generally not water soluble.

In one non-limiting explanation, when very small pyroelectric crystals,such as nano-sized ZnO, are added to a base fluid, which is then pumpeddownhole into underground formations that are under high temperatureand/or pressure, the pyroelectric crystals are heated and/or pressed andhigh surface charges are generated. These surface charges permit thecrystal particles to associate, link, connect or otherwise relate theformation fines together to fixate them together and also to the carrierparticles.

It should be noted that dual-function nanoparticles may be used alone orin combinations or mixtures. For instance and without limitation, thealkaline earth metal oxides and hydroxides, may be used alone or incombination with one or more transition metal oxide, transition metalhydroxide, post-transition metal oxide, post-transition metal hydroxide,piezoelectric crystal, and pyroelectric crystal.

In some embodiments the dual-function nano-sized particles may be taggedwith a taggant material. For nanoparticles of a given composition, theassociated taggant should be distinguishable from the nanoparticleprimary component. As a non-limiting example, the primary component ofthe dual-function nanoparticles may be a mixture of different oxidephases, such as MgO, CaO, SiO₂, Al₂O₃ and the like, the majority ofwhich being MgO. The exact choice of taggant for association with suchprimary component could also be an oxide phase albeit one with acomposition distinguishable from other phases that may be part of thesystem.

It is believed that suitable taggants may be selected from the groupconsisting of alkaline earth metals, transition metals, post-transitionmetals, lanthanoids, and mixtures thereof. Of the alkaline earth metals,Sr and Ba are two non-limiting examples of suitable taggants.Non-limiting examples of suitable transition metal taggants includescandium (Sc), yttrium (Y), Ti, Zr, hafnium (Hf), vanadium (V), niobium(Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), manganese (Mn),rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), Co, rhodium (Rh),iridium (Ir), Ni, palladium (Pd), platinum (Pt), copper (Cu), silver(Ag), gold (Au), Zn, cadmium (Cd), and mixtures thereof. Of thepost-transition metals a taggant may be selected, without limitation,from the group consisting of: Al, Ga, In, Th, germanium (Ge), Sn, Pb,arsenic (As), antimony (Sb), Bi, selenium (Se), tellurium (Te), andmixtures thereof. Furthermore, lanthanoid-based taggants may be selectedfrom the group consisting of: lanthanum (La), cerium (Ce), praseodymium(Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu),gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium(Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and mixtures thereof.

One or more taggants may be included with, added to, or coated on theprimary component of the nanoparticles. Although taggant may occur inelemental form, it is more likely that the taggants occur as compounds.Non-limiting examples of potential types of compounds include fluorides,chlorides, bromides, nitrates, nitrides, iodates, oxides, hydroxides,carbonates, sulfates, sulfides, phosphates, silicates, alkoxides,organic acids such as manganese gluconate, and combinations thereof. Itshould be noted that the taggant may not remain in its original form; itmay be modified such as during processing. For example, during coatingprocesses the taggant may be modified by a reducing agent, changedduring vapor phase for deposition, or altered by interacting with aliquid phase if slurried or dissolved.

In some non-limiting embodiments, taggant may be added duringmanufacture of nano-sized particles. For instance, the taggant may becontinuously distributed along the entire nano-sized particle. In a nonlimiting example, Zn, or a zinc compound, may be added to a solutionfrom which MgO nano-sized particles are produced so that the end productconsists of Zn doped MgO. Nano-sized particles of similar compositionmay also be produced by using vapor phase processes.

In other non-limiting embodiments, the nanoparticles manufacturingprocess may consist of two of more sequential steps resulting incore-shell structure. For instance, the taggant material may form thecore of the nanoparticles, which has a structure consisting of a coreand an outer layer of a different material such as the primarycomponent. In this configuration the taggant material does not enter incontact with the formation or liquid phase. Core-shell nanoparticles canbe fabricated either by solution chemistry route or by vapor depositionroute. A non-limiting example of a core-shell nano-sized particle is theone where a magnetic core is surrounded by MgO. The magnetic core alsoeases separation of nanoparticles from the suspension by an appliedmagnetic field. In this alternative, non-restrictive embodiment, thecore-coating nanoparticles will behave as regular MgO nanoparticles interms of fine adhesion. The magnetic core may be used to separate theparticles from the suspension for analysis or for direct identification,for instance if particles with the magnetic core are placed in one zoneand particles without the magnetic core are placed in another zone.

In other non-limiting embodiments, the nanoparticles may be taggedpost-manufacture such as by coating them with a coating material thatincludes the taggant. Any suitable coating technique may be used to coatthe nanoparticles such as without limitation, molten salt, plasmacoating, chemical vapor deposition (CVD), physical vapor deposition(PVD), chemical and electrochemical techniques such as withoutlimitation electroless plating, and the like. In one non-limitingexample coating may take place by electroless plating using one or moreeasily reducible metals. In another example, a very thin film of thetaggant material may be deposited on the nano-sized particles. Suchdeposition may take place by chemical vapor deposition processes (CVD)or physical vapor deposition (PVD) in which the precursors for thetaggant are supplied from the vapor phase, and the nanoparticles are ina fluidized state. In order to assist the activation of the precursorsduring chemical vapor deposition, the process deposition process maymake use of a plasma.

Regardless of how the taggant is coated or deposited on thedual-function nanoparticles, the coating may be a low density or partialcoating, a complete coating encapsulating individual nanoparticles, or acombination of partial and completely coated nanoparticles. In yet otherembodiments coated dual-function nanoparticles, whether partially and/orcompletely coated, are mixed with nanoparticles that are not coated. Ina specific, non-limiting example, from about 0.5% to about 10% by weightof the total nanoparticles added to proppant or within a fluid such as atreatment fluid are coated with a taggant.

In another non-limiting embodiment, the dual-function nanoparticles mayhave a particle size of from about 1 nanometer independently up to about1000 nanometers regardless of the presence or absence of taggant. Inanother non-limiting embodiment, the particle size may range from about10 nanometers independently up to about 500 nanometers. In anothernon-restrictive version, the dual-function particles may have a meanparticle size of about 400 nm or less, alternatively about 300 nm orless, and in another possible version about 200 nm or less,alternatively 100 nm or less.

As has been previously mentioned, dual-function nano-sized particles maybe disposed on carrier particles such as proppant, gravel, or the like.In other embodiments, however, dual-function nano-particles may bepumped downhole in a base fluid or a carrier fluid as a particulateadditive, where the base fluid or carrier fluid also contains proppantor gravel particles. The amount of dual-function nano-sized particles inthe base or carrier fluid may range from about 20 to about 500 poundsper thousand gallons (pptg) (about 2.4 to about 60 kg/1000 liters).Alternatively, the lower threshold of the proportion range may be about50 pptg (about 6 kg/1000 liters), while the upper threshold ofproportion of the particles may independently be about 300 pptg (about36 kg/1000 liters).

The base fluid may be water-based, alcohol-based or oil-based, but inmany embodiments the base fluid is expected to be water-based.Non-limiting examples of suitable water-based fluids include, but arenot restricted to, EMERALD FRAQ® aqueous fluid containing a crosslinkedpolymer and DIAMOND FRAQ™ aqueous fluid containing a viscoelasticsurfactant (VES), both available from Baker Hughes Incorporated. Inanother non-restrictive version, the base fluid may be foamed.

The base fluid or aqueous-based fluid may be a brine. In non-limitingembodiments, the brine may be prepared using salts including, but notnecessarily limited to, NaCl, KCl, CaCl₂, MgCl₂, NH₄Cl, CaBr₂, NaBr,sodium formate, potassium formate, and other commonly used stimulationand completion brine salts. The concentration of the salts to preparethe brines may be from about 0.5% by weight of water up to nearsaturation for a given salt in fresh water, such as 10° A, 20%, 30% andhigher percent salt by weight of water. The brine may be a combinationof one or more of the mentioned salts, such as a brine prepared usingNaCl and CaCl₂ or NaCl, CaCl₂, and CaBr₂ as non-limiting examples.

While the fluids herein are sometimes described typically herein ashaving use in fracturing fluids, it is expected that they will findutility in gravel pack fluids, displacement fluids and the like. In thecase where the carrier fluid is an acidizing fluid, it also contains anacid. In the case where the carrier fluid is also a gravel pack fluid,the fluid also contains gravel consistent with industry practice.

In hydraulic fracturing applications, propping agents, or proppants aretypically added to the base fluid. The propping agents are normally usedin concentrations between about 1 to 14 pounds per gallon (120-1700kg/m³) of fracturing fluid composition, but higher or lowerconcentrations may be used as the fracture design requires. The proppantmay carry or have disposed thereon dual function nanoparticles.

In addition to proppant, dual-function nanoparticles may be carried byor disposed on gravel, solid particles, or the like. These dualfunction, nano-particle carrier particles may be any particulate mattersuitable for its intended purpose, for example as a screen or proppant,etc. Suitable materials include, but are not necessarily limited to sand(e.g. quartz sand grains), sintered bauxite, bauxite grains, walnutshell fragments, aluminum pellets, nylon pellets, sized calciumcarbonate, other sized salts, glass and/or ceramic beads, and the like,and combinations thereof. In a non-limiting embodiment, the proppantparticles may be 20/40 mesh ceramic proppants. These solids may also beused in a fluid loss control application.

In a non-limiting version, dual-function nanoparticles may be coated oncarrier particles such as a proppant or sand. In one embodiment, a finescontrol agent, which includes a mixture of a coating agent and thedual-function nanoparticles, may at least partially coat a proppant (orother suitable carrier particle) to fixate formation fines within aproppant pack or other porous media, or inhibit or prevent fines frommigrating or moving within the subterranean formation. In anothernon-limiting embodiment, if gravel is at least partially coated with thefines control agent then the formation fines may be fixated within thegravel pack, or they may be inhibited from migrating or moving withinthe subterranean formation. In these non-restrictive examples, if theproppant pack or gravel pack fails, the carrier particles together withthe dual-function nanoparticles may flow back into the wellbore.

It is expected that at least a portion of carrier particles such asproppant may be “pre-coated” with the fines control agent; for instance,a select portion of the proppant may be pre-coated before the job. As anon-restrictive example, pre-coating may be performed at themanufacturing site of the dry proppant or elsewhere. In onenon-restrictive version, the fines control agent may be possibly sprayedonto the dry proppant (or other carrier particles) before the proppantis placed in an aqueous treatment fluid. In another non-limitingembodiment, the fines control agent may be coated on proppant or sandduring placement downhole.

In addition to one or more embodiments of dual-function nanoparticles,the fines control agent may also include a coating agent. Suitablecoating agents include, but are not necessarily limited to, mineral oilor other suitable hydrocarbon. Specific, non-limiting examples ofsuitable mineral oils include ConocoPhillips Pure Performance® Base Oil,such as 225N and 600N oils. In some embodiments, a fines control agentmay include dual-function nanoparticles in the coating agent oil, forinstance about 15 wt % nano-sized, tagged MgO particles in the 600Nmineral oil. This type of fines control product may be added to anaqueous base fluid in a relatively small amount, in one non-limitingembodiment, from about 5 to about 100 gallons per thousand gallons(gptg). (Equivalent SI proportions may be any convenient volume with thesame value, e.g. about 5 to about 100 liters per thousand liters orabout 5 to about 100 m³ per thousand m³.) During mixing, the finescontrol product (i.e. the dual-function nanoparticles in oil) may plateout on or at least partially coat the carrier particles in the basefluid, such as proppant particles. That is, since the base fluid isaqueous, the hydrophobic oil will be repulsed by the water and will coatthe carrier particles (e.g. proppant). How much coating of the carrierparticles that occurs is concentration dependant, based on both theamount of carrier particles used and the amount of fines control productused. In a non-limiting example the fines control product mayadditionally have a surfactant present, such as an oil-wettingsurfactant like sorbitan monooleate Span 80 from Uniqema), to improveand/or enhance the oil-wetting of the proppant particles by the finescontrol product. In another non-limiting example the presence of asurfactant may preferentially reduce the thickness of the 600N mineraloil layer on proppant particles. Reduced oil layer thickness may enhancedual-function nanoparticle exposure on proppant particles. Other agentsbesides Span 80 may be employed to optimize the oil coating or wettingon proppant particles, agents such as: sorbitan esters, ethoxylatedsorbitan esters, ethoxylated alcohols, ethoxylated alkyl-phenols,alkyl-dicarboxylics, sulfosuccinates, phospholipids, alkyl-amines,quaternary amines, alkyl-siloxanes, and the like. It is not necessarythat a resin be used as a coating agent or binder, and in onenon-limiting embodiment, no resin is used.

Mineral oil may be a particularly suitable coating agent for at leasttwo reasons. First, mineral oil and like substances may have an affinityto coat carrier particles such as proppant particles as contrasted withremaining as oil droplets containing dual-function nanoparticles as aphase internal to the water-based fluid. It is believed that the moststable configuration for the fines control agent once placed in anaqueous treatment fluid is to “plate out” or coat or at least partiallycoat the carrier particles. Second, a high molecular weight mineral oilcoating agent may not disturb the fluid properties of an aqueous fluidcontaining a polymer gelling agent or a VES gelling agent, and thus itmay be ideal for depositing the dual-function nanoparticles onto theproppant without disturbing aqueous fluid properties.

It is theorized that the dual-function nanoparticles remain on theproppant particles primarily by electrostatic and other charges betweenthe nanoparticle and proppant particle surfaces, however, otherattractions or coupling forces may exist to initially and over thelong-term keep the nanoparticles coated on the proppant particles. Theinventors, however, do not want to be limited to any particular theory.It is suspected that in most conditions the oil carrier fluid onlyassists the initial coating process of the dual-function nanoparticlesonto the proppant particles. Other agents, however, may be added to theoil carrier fluid to further enhance initial and/or long-termnanoparticle attraction to particles including, without limitation,quartz, glass, ceramic and other materials known in the proppant art.Additionally, the surface of the proppant, or a select amount ofproppant, may be treated with agents that may improve the overallattraction of the dual-function nanoparticles to proppant or othercarrier particles.

In the foregoing specification, it will be evident that variousmodifications and changes may be made thereto without departing from thebroader spirit or scope of the invention as set forth in the appendedclaims. Accordingly, the specification is to be regarded in anillustrative rather than a restrictive sense. For example, specificcombinations of alkaline earth metal oxides, alkaline earth metalhydroxides, transition metal oxides, transition metal hydroxides,post-transition metal oxides, post-transition metal hydroxides,piezoelectric crystals, and pyroelectric crystals, of various sizes;brines; base fluids; proppants (sand, ceramic or glass beads, gravel);coating agents (oils); taggants (including specific combinations oftaggants and taggant-primary component combinations) and othercomponents falling within the claimed parameters, but not specificallyidentified or tried in a particular composition or method, areanticipated to be within the scope of this invention.

The present invention may suitably comprise, consist or consistessentially of the elements disclosed and may be practiced in theabsence of an element not disclosed. For instance, the coated carrierparticles may consist of or consist essentially of the carrierparticles, nanoparticles and a taggant, as further defined in theclaims. Alternatively, the drilling fluid may consist of or consistessentially of the base fluid, the nanoparticles and a surfactant, asfurther defined in the claims. In each of these examples, the drillingfluid may contain conventional additives.

The words “comprising” and “comprises” as used throughout the claims isto interpreted “including but not limited to”.

What is claimed is:
 1. A treatment fluid for reducing fines migrationand comprising: a base fluid selected from the group consisting ofwater-based fluids, alcohol-based fluids and oil-based fluids, andcoated carrier particles consisting of: carrier particles, an effectiveamount of a particulate additive coated on the carrier particles toreduce fines migration and to facilitate identification of a zone in awell having more than one treatment-based zone, and taggants coated onthe particulate additive; wherein the carrier particles are selectedfrom the group consisting of sand, gravel, ceramic beads, glass beads,and combinations thereof; wherein the particulate additive has a meanparticle size of 1000 nm or less and is selected from the groupconsisting of alkaline earth metal oxides, alkaline earth metalhydroxides, transition metal oxides, transition metal hydroxides,post-transition metal oxides, post-transition metal hydroxides,piezoelectric crystals, pyroelectric crystals, and mixtures thereof; andwherein the taggant is selected from the group consisting of alkalineearth metals, transition metals, post-transition metals, lanthanoids;and mixtures thereof, where the taggant is selected to bedistinguishable from the primary component.
 2. The treatment fluid ofclaim 1 where the alkaline earth metal is selected from the groupconsisting of magnesium, calcium, strontium, and barium, and mixturesthereof, the transition metal is selected from the group consisting oftitanium, and zinc and mixtures thereof, and the post-transition metalis aluminum.
 3. The treatment fluid of claim 1 where the taggantalkaline earth metal is selected from the group consisting of strontium,barium, and mixtures thereof; the taggant transition metal is selectedfrom the group consisting of scandium, yttrium, titanium, zirconium,hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten,manganese, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium,nickel, palladium, platinum, copper, silver, gold, zinc, cadmium, andmixtures thereof; the taggant post transition metal is selected from thegroup consisting of aluminum, gallium, indium, thallium, tin, lead,bismuth, germanium, arsenic, antimony, selenium, tellurium, and mixturesthereof; and the taggant lanthanoid is selected from the groupconsisting of lanthanum, cerium, praseodymium, neodymium, promethium,samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium,thulium, ytterbium, lutetium, and mixtures thereof.
 4. The treatmentfluid of claim 1 where, to reduce fines migration, the effective amountof the particulate additive ranges from about 20 to about 500 pptg(about 24 to about 60 kg/1000 liters) based on the aqueous treatingfluid.
 5. The treatment fluid of claim 1 where the base fluid isselected from the group consisting of a fracturing fluid, a gravel packfluid, and a frac pack fluid.
 6. The treatment fluid of claim 1 wherethe base fluid also includes taggant-free particulate additive, andwhere the particulate additive having a taggant is from about 0.5% toabout 10% by weight of the total particulate additive.